Measuring sensor

ABSTRACT

Measuring sensor to measure a gas, comprising: a housing having an inlet opening for the gas to be measured, a sensor chip located within said housing and having a sensor element at one end area of the sensor chip facing the inlet opening and an electrical connection connected electrically with the sensor element provided at another and, and with at least one contact trace which is electrically conducting, wherein the electrical connection is joined to the contact trace by laser welding.

This is a continuation of application Ser. No. 08/669,361, filed Aug.28, 1996 now abandoned, which is a 371 of PCT International ApplicationNo. PCT/EP95/00042, filed Jan. 5, 1995.

The invention relates to a measuring sensor according to the preamble ofthe main claim.

Measuring sensors of this kind are known for example as lambda sensorsin a plurality of embodiments. All sensors suffer from the problem thatfirstly they must have an opening through which the gas to be measuredcan enter and reach the sensor chip itself, and secondly they must bemade gas-tight in order to prevent the measured gas from escaping at theplace where the measuring sensor is preferably screwed in place. Inparticular however, the mechanical mounting of the sensor chip in thehot and pulsating exhaust of internal combustion engines and the thermalloadability of the electrical connection pose problems.

Hence, the goal of the invention is to design a measuring sensoraccording to the species in a simple fashion with sufficient mechanicalas well as thermal loadability.

This goal is achieved in a measuring sensor according to the species andaccording to the preamble of the main claim by its characterizingfeatures according to the invention.

The measuring sensor is therefore disposed according to the teaching ofthe invention in a housing in which the electrical and mechanicalconnection of the sensor chip, which contains a ceramic, preferably Al₂O₃, is performed by direct or indirect laser welding to the trace ortraces of the sensor chip.

An advantageous embodiment and improvements on the invention arecharacterized in the subclaims.

The measuring sensor itself, according to the teaching of the invention,can be located in a cylindrical or metallic housing into which theelectrical connection, in the form of an internal conductor surroundedby a metal jacket tube, hereinafter referred to as the metal jacket leadfor short, is introduced, the metal jacket of said lead being connecteddirectly or indirectly with the metal housing by welding or soldering.Preferably, the metal jacket lead is introduced into the tubular housingfrom one end, into the tube which is open at that location. The internalelectrical conductor in the metal jacket lead can be embedded in anelectrical insulator, MgO for example, inside the metal jacket tube. Themetal jacket tube provides an absolutely gas-tight feedthrough for theelectrical connecting wires from the housing. In this design, the sensorchip can also be secured purely mechanically at one end by the more orless rigidly acting internal conductor of the metal jacket lead,directly or indirectly. An appropriate choice of material for theinternal conductor, for example an alloy containing copper and/oraluminum and/or iron and/or nickel and/or chromium, also ensures highthermal loadability.

According to one especially preferred embodiment, the electricalconnection has a clip that is pushed laterally in a mechanicallyclamping fashion onto both the top and bottom of the sensor chip, overits edge on the long side of the sensor chip that is made plane, andrests firmly and with zero play on the contact trace. The clip islaser-welded to the contact trace of the sensor chip, which preferablyconsists of a noble metal, platinum for example, and is mounted on thesubstrate of the sensor chip by means of an adhesion promoter. Theadhesion promoter preferably contains the same noble metal as thecontact trace, as well as glass and/or ceramic components. The clip alsohas a contact tab extending toward the insertion opening, said tab beingbent into the shape of a U for the purpose of thermal lengthcompensation and also being in the form of a strip. One of theconnecting wires of the internal conductor is connected to theconnecting tab, also preferably by laser welding. As a result of theU-shaped bend, an additional clip can be placed in the area between thetwo legs of the U on another contact trace of the sensor chip, so thatfour clips can be applied without difficulty.

In an open system (FIG. 3) the electrical connecting wires of theinternal conductor which are brought out from the metal jacket lead canbe exposed directly to the hot exhaust, from an internal combustionengine for example, and must therefore consist either of surface-refinedlead wires or solid oxidation-resistant materials. Preferably, however,a half-open system is used in the invention (FIGS. 1 and 2), in which asupporting element that supports the chip additionally is providedbetween the electrical connecting wires and the actual part of thesensor chip that bears the sensor element. In addition, the supportingelement, when it is in the form of a preshaped wire knit, can alsocapture particles of dirt or the like that are present in the gas, sothat they cannot reach the vicinity of the insertion opening.

In another embodiment of the invention, the electrical connecting wirescan be guided in an arc from the metal jacket lead to the sensor chipitself and can thus compensate for tensile forces and equalize thermalexpansion. Depending on the length of the electrical leads, they canalso have a highly conductive core, made of copper or silver forexample. The connecting wires can be attached for example by directcontact of these wires (possibly with previous shaping and also withshaping of the arc) with the contact trace of the sensor chip, but alsocan be connected by means of a connecting sleeve. Direct contact withthe substrate is always produced by laser welding. In all othercontacts, for example indirect (including non-electrical) contacts, onthe other hand, other welding methods may be used. The connecting sleeveis guided over the connecting tab and over the ends of the electricalconnecting wires, and can likewise consist of ahigh-temperature-resistant and corrosion-proof material. Theoxidation-prone open ends of the two connecting wires are tightly sealedby the subsequent welding. Corrosion of the open ends of the connectinglead can likewise be suppressed by the protective sleeve of the wirecore being machined to overlap and fit snugly, resulting ingas-tightness. In the prior art, the sensor chip itself is alwaysconnected to the electrical connection and the sensor element is alwaysmounted in the vicinity of a part of the housing that is alreadyseparated in a gas-tight manner, so that considerable expense may beinvolved in sealing.

In addition, the sensor chip can be metallized on one side for improvedhandling during the manufacturing process, to which metallization one ormore small feet of small legs of a retaining part can be welded, saidmetallization generally being connected by a link with the metal jackettube introduced into the interior of the housing of the measuringsensor, preferably by welding. Thus, even during the manufacturingprocess, there is a certain stability of the individual parts to beconnected together. In addition, there is a definite anchor for thesensor chip itself. An increase in the length of the sensor chip as aresult of thermal expansion beyond the length that is in contact can becompensated by this type of small leg of the retaining part that runs atright angles to the length of the sensor chip by virtue of the fact thatthe small legs can pivot through a small angle. The different expansionsover the length of the contact between the sensor chip and the retainingpart are mechanically relieved from the standpoint of thermal stress bythe small legs.

The small legs in this case are mounted on one end of the sensor chip.The other end can also be held in place by a connection having one ormore small legs, with the small feet provided at the ends of the smalllegs pointing away at right angles from the sensor chip itself and thenbeing directed at right angles once more along the length of the tubularhousing of the measuring sensor. By means of a resultant V-shaped bend,permanently welded at its free end to the inside of the housing, firstlya secure mounting of the sensor chip itself is obtained and secondly theV-shaped design permits safe thermal expansion without damage to thesensor chip. Both mounts are also preferably made of ahigh-temperature-resistant as well as corrosion-resistant material, forexample the same material as the housing of the sensor chip. Both areasof the mechanical mount abutting the small feet are located at adistance from the interior of the tubular metal housing of the measuringsensor. In general, this results in a good mechanical connection firstlyto the sensor chip itself and secondly to the metal housing of themeasuring sensor. Moreover, if the same materials are used, an identicalthermal coefficient of expansion advantageously results. Finally, it ispossible for the small feet not only to be located on one side of thesensor chip itself but also to fit around its edge at least partiallyand/or partially engage or fit into or over recesses in the vicinity ofthe edge of the sensor chip, so that a firm mechanical mount is achievedby virtue of an additional positive or nonpositive fit.

The fact that practically all the individual parts to be connected withone another can be joined by laser welding is especially advantageous.

In open as well as half-open systems, the response time of the sensorcan be adjusted by additionally providing openings on the circumferenceof the anterior area of the housing. In addition, the anterior holder ofthe sensor chip in the open version can be designed simultaneously as amechanical protection for the sensor element. By changing the positionof the collar mounted on the housing as a counterbearing for a unionnut, the installation depth of the measuring sensor can be varied in avery simple fashion.

In summary then, it is clear that in the preferred embodiment both theelectrical and mechanical connections of the sensor chip are made by theclips that rest flush on its contact traces and are connected in thisarea by laser welding, with the connecting wires of the internalconductor of the metal jacket lead likewise being welded to theconnecting tabs of said clips, resulting in an especially simple andlogical solution.

Embodiments of the invention will now be described in greater detailwith reference to the drawing.

FIG. 1 shows a schematic cross section through a first embodiment of themeasuring sensor;

FIG. 2 is a section II--II according to FIG. 1;

FIG. 3 is a second embodiment of the invention; and

FIG. 4 is a third embodiment of the invention in a top view.

FIG. 5 shows the embodiment in FIG. 4 in a side view;

FIG. 6 is a section VI--VI according to FIG. 5;

FIG. 7 shows detail VII according to FIG. 3; and

FIG. 8 shows detail VIII according to FIG. 6, schematically and on anenlarged scale.

The first embodiment (FIGS. 1 and 2) of a measuring sensor, designatedas a whole by 10 in FIG. 1, has a housing designed as a cylindrical tube11 made of a metallic material, one of whose sides, facing the gas to bemeasured, has an open end with an inlet opening 12 and at the other endhas an electrical connection 13 designed as a metal jacket lead, saidlead 13 being provided with a mounted bushing 14 firstly connected withthe outer tube of the metal jacket lead by means of a laser-weldedconnection 15 and by means of a weld 16 with the open end of tube 11.

A union nut 17 is provided in the central area, said nut serving toscrew the entire measuring sensor into a measuring opening over a collar27 that serves as a counterbearing, said collar likewise being connectedwith tube 11 by welding.

The actual sensor element 19 of sensor chip 18, which extends in thelengthwise direction of the tube, is located at the forward end of tube11, in its area facing inlet opening 12. Between the actual sensorelement 19 and the end of the sensor chip 18 on the connecting side, asupporting support part 20, made of a correspondingly shaped and/orpreshaped wire knit, is pushed onto it. As a result, the sensor chip isfirstly held mechanically in its area facing inlet opening 12 at rightangles to the length of the tube. On the other hand, particles and thelike contained in the exhaust cannot penetrate to the vicinity of theelectrical connection of the metal jacket lead 13.

In the first and second embodiments (FIGS. 3 and 7) a holding part isprovided in the area of sensor chip 18 facing away from actual sensorelement 19 and is designated as a whole by 21. This holding part runsessentially parallel to the length of tube 11. Small legs 22 projectfrom it at right angles, said legs being provided at their ends withsmall feet 23 (FIG. 7). The side of sensor chip 18 at the bottom in FIG.7 has a metallization designated as a whole by 24, to which small feet23 of the holder designated as a whole by 21 are welded. In addition,holding part 21 can also be connected by welding or soldering with asurrounding piece 25 bent around a bend 26 in the shape of a partialcylinder jacket, likewise by welding with the outer tube of metal jacketlead 13.

Instead of wire knit 20 in the second embodiment according to FIG. 3, aholding part 30 roughly corresponding to retaining part 21 can beprovided in the forward part, said holding part likewise being providedat its end with small legs that likewise run transversely to its length,preferably at right angles, with small feet provided at its end, saidfeet being connected at metallization 24 with the underside of sensorchip 18 by laser welding. This holding part 30 is provided with aV-shaped bend 31 whose tip 32 is located at a distance from the oppositeinterior of tube 11. The outermost end 33 of this holding part 30 issecured to the inside of tube 11, for example by welding. The differencein lengthwise thermal expansion between tube 11 and the entire length ofsensor chip 18 is compensated by the V-shaped bend 31.

The electrical connection of sensor chip 18 that carries actual sensorelement 19 can be provided either by virtue of the fact that eitherconnecting wires 40 of metal jacket lead 13 are welded directly to thesensor chip (FIG. 1) or are connected electrically with one another bymeans of connecting tabs 41 mounted on sensor chip 18 (FIGS. 3, 4 to 6,and 8) and possibly by a connecting sleeve 42. In both cases theconnecting wires are preshaped in such fashion (for example in the formof an arc 43 that serves to relieve tension) and are shaped in theconnecting area to the substrate transversely to the length in suchfashion that an at least areawise flat support results.

A third, completely preferred embodiment with an electrically conductingclip 50 is shown in FIGS. 4 to 6 (without the housing) and in 8 as ahalf-open system with supporting support part 20, and has the advantagethat the clip has a double function, namely as an electrical connectionand as a mechanical holder. The clip has a connecting tab 41 that has aU-shaped bend 54, said tab also being made in the form of a strip, andis mounted by one lengthwise edge of plane sensor chip 18 in suchfashion that the two flexible arms 55, 56 of clip 50 rest firmly andflush on both the top and bottom of the sensor chip.

Actual connecting tab 41 begins behind U-shaped bend 54 in theembodiment shown, said tab in turn resting on the surface of sensor chip18, so that the stiffness of this arrangement is increased. A connectingwire 40 of the internal conductor of metal jacket lead 13 is connectedto this connecting tab 41, preferably by laser welding. In the vicinityof U-shaped bend 54 of one clip, the two arms of another clip can beapplied laterally, the U-shaped bend of said clip being located on theother side of the sensor chip.

On substrate 53, e.g. Al₂ O₃ of sensor chip 18, an adhesion-promotinglayer 52 is also applied by screen printing and a layer containingplatinum is provided on top of this layer, likewise by screen printing,as a contact trace 51. One arm 56 of clip 50 rests on this trace, saidarm being welded by laser welding to contact trace 51, as indicatedschematically by 57.

We claim:
 1. A method for making a measuring sensor for measuring hotfluid, which comprises the steps of:providing a housing having an inletopening for the fluid to be measured; providing a sensor chip; saidsensor chip providing step including the steps of providing a ceramicsubstrate and providing an electrically conductive contact trace on saidceramic substrate; positioning said sensor chip within said housing,said sensor chip having a sensor element at one end area of the sensorchip toward said inlet opening; and laser welding an electricallyconductive lead to said contact trace at a location within said housing.2. A method as defined in claim 1, including the step of providing saidelectrically conductive lead with a flexible portion to provide lengthcompensation and/or tension relief.
 3. A method for making a measuringsensor for measuring hot fluid, which comprises the steps of:providing ahousing having an inlet opening for the fluid to be measured; providinga sensor chip; said sensor chip providing step including the steps ofproviding a ceramic substrate and providing an electrically conductivecontact trace on said ceramic substrate; positioning said sensor chipwithin said housing, said sensor chip having a sensor element at one endarea of the sensor chip toward said inlet opening at a location wherethe sensor chip will be exposed to high temperatures; and laser weldingan electrically conductive lead to said contact trace at a locationwithin said housing where the laser weld will be exposed to hightemperatures.
 4. A method for making a measuring sensor for measuringhot fluid, which comprises the steps of:providing a housing having aninlet opening for the fluid to be measured; providing a sensor chip;said sensor chip providing step including the steps of providing aceramic substrate and providing an electrically conductive contact traceon said ceramic substrate; positioning said sensor chip within saidhousing, said sensor chip having a sensor element at one end area of thesensor chip toward said inlet opening; welding one location of anelectrically conductive lead to said contact trace; providing anelectrically conductive connecting element at another location of saidelectrically conductive lead; providing a metal jacket lead with aninternal conductor insulated from said metal jacket by a mineral; andlaser welding said internal conductor to said connecting element at aposition within said housing.
 5. A method as defined in claim 4,including the step of welding said metal jacket to said housing in agas-tight manner.
 6. A measuring sensor for measuring hot fluid, whichcomprises:a housing having an inlet opening for the fluid to bemeasured; a sensor chip; said sensor chip including a ceramic substrateand an electrically conductive contact trace on said ceramic substrate;said sensor chip being located within said housing, said sensor chiphaving a sensor element at one end area of the sensor chip towards saidinlet opening; and an electrically conductive lead laser welded to saidcontact trace at a location within said housing.
 7. A measuring sensorfor measuring hot fluid, which comprises:a housing having an inletopening for the fluid to be measured; a sensor chip; said sensor chipincluding a ceramic substrate and an electrically conductive contacttrace on said ceramic substrate; said sensor chip being located withinsaid housing, said sensor chip having a sensor element at one end areaof the sensor chip towards said inlet opening at a location where thesensor chip will be exposed to high temperatures; and an electricallyconductive lead laser welded to said contact trace at a location withinsaid housing where the laser weld will be exposed to high temperatures.